Typically, media is advanced through a printer using a drive roller or feed roller. These generally cylindrical drive rollers advance media through the printer along a media path as the drive roller rotates about a drive shaft driven by a motor. Conventional drive roller mechanisms are susceptible to linefeed errors that cause paper-positioning inaccuracies. With the advent of more complex print jobs, paper-positioning accuracy has become increasingly important. To ensure paper-positioning accuracy, the drive roller advancing mechanism must be regulated to meet increased precision requirements and overcome problems associated with linefeed errors.
Linefeed errors can be characterized in at least two ways, run-out error and diametrical error. Run-out error is due to undesired eccentric rotation of the drive roller Diametrical error is due to a change in the diameter of the drive roller itself. Both types of error are caused by inaccuracies in the manufacture of drive rollers, and the result causes linefeed advance to be off by increments typically approximating less than 1/600 of an inch. Accordingly, manufacturing inaccuracies of drive rollers have presented a special problem in view of current printing requirements.
By identifying inaccuracies in media advancement due to the drive roller, the printer may be calibrated such that it adjusts and compensates for such inaccuracies. However, known linefeed calibration processes typically are expensive, and limited in their application. For example, one process includes using a pre-printed, pre-measured page, which is fed through a printer having a sensor that measures a distance between markings on the pre-printed page. The printer then compares the measured distance with a pre-measured, reference distance, and uses that comparison to determine whether the printer over- or under-advanced after each linefeed. Data identifying such over- or under-advancement is then stored in memory, and used to adjust linefeed advance. One problem with this calibration process is that it is based upon pre-printed media, which may not be of the same media type that the user may actually use in the printer. Moreover, the process only responds to an approximation of the problem because comparison of measured and reference distances occurs during manufacture of the printer and not in the actual user environment.
A second calibration process uses a calibration page that is printed by a printer, but then must be removed and placed in a scanner to measure print errors. This process is not desired because the requirement of using both a printer and a scanner increases production time and does not allow the printer to be tested in the actual user's environment.
What is needed is a process of calibrating linefeed in the user's environment with the user's choice of media. By providing a linefeed calibration process that can be completed by the user, production time and costs could be decreased during the manufacture process. Moreover, the ability of the user to calibrate a printer in the user environment will eliminate any errors due to variations between the manufacturer's environment and the user environment.